Why does everybody think that they need to watch their salt intake?

The history of salt intake recommendations

Nutrition is extremely difficult to study. With so many variables at play, the ability to come to conclusive findings is quite constrained. Context plays such an important role in the interpretation of nutrition findings in studies and people are only now really starting to understand how nuanced this field is.

The problem is that much of our standard nutrition advice is based on research findings from around the 1960s when nutrition research was really in its infancy. The standard method of understanding nutrition was observing the food intake of populations and correlating that with their health outcomes. In my post on red meat, I talked about some of the flaws in observational research. Much of the same flaws exist in salt intake guidelines.

There are a few key researchers that looked at observational data regarding salt. Lewis Dahl was one of the largest proponents of salt being harmful to blood pressure. He took 6 countries and found that hypertension was more common in societies with higher-than-average salt intakes [1]. This led to the dietary goals in 1977 that everyone should be on a low-salt diet, which got translated into the 1980 dietary guidelines and has been continued ever since, without ever really questioning where this evidence stems from.

However, in order for Lewis Dahl to prove his hypothesis in labs, he had to create salt-sensitive rats for salt to increase blood pressure chronically because he couldn’t do it with a normal population of rats [2]. Decades later, the Intersalt study was done where they looked at 48 countries and did not find a clear pattern between the level of salt intake and blood pressure [3]. In fact, there was a trend down – as salt increased to a normal amount, blood pressure decreased.

In 2005 the American Heart Association started recommending less than half a teaspoon of salt per day. These recommendations are now slowly starting to get less restrictive because of the studies coming out showing that higher urinary sodium excretion, which is an indicator of sodium intake, is actually associated with the lowest risk of dying from cardiovascular disease [4][5]. Low-salt intake has also been associated with worse health outcomes in diabetes [6][7] and salt restriction has been shown to be particularly dangerous for the elderly. Elderly people with hyponatremia (below normal levels of sodium in the blood) have more falls, unsteadiness, and attention deficits [8].

What are the health benefits of salt?

Salt is made up of two essential minerals – sodium and chloride. Chloride helps make up hydrochloric acid which is needed to digest food and absorb nutrients. It also inhibits and kills pathogens. Insufficient chloride can reduce stomach acid and increase the PH of the stomach. Reducing stomach acid increases the risk of pathogens entering the body and can cause numerous nutrient depletions since food can’t be absorbed as well.

Sodium is used for maintaining electrical currents in the body. This is important so that the muscles don’t spasm so that the heart beats and gives us adequate blood pressure. Maintaining adequate blood pressure is extremely important for transporting nutrients and waste products throughout our bodies. When blood pressure is reduced, our stress hormones are increased [9]. The RAAS (renin-angiotensin-aldosterone system) is a hormonal system that regulates blood pressure in the body. It responds when there is too little salt and/or blood pressure and does what it can to try to bring the body back to a normal state.

This system allows us to maintain adequate sodium levels in our blood by reducing the amount excreted in our kidneys. However, this results in a greater loss of potassium and magnesium [10]. Chronic loss of these electrolytes can lead to high blood pressure and restrict our ability to produce energy.

Salt plays an important role in hormone health. Low salt is a stressor on the adrenal glands because they must constantly produce aldosterone to retain salt [7]. This can lead to hypertrophy of the adrenal glands, which can eventually lead to burnout. A lot of fatigue and issues with hormone function can be caused by low salt. We also need sodium to pull iodine into the thyroid gland [11]. Insufficient iodine can decrease thyroid hormone production and can lead to hypothyroidism.

Salt can also play a major role in mental health, including depression and anxiety. Almost every neurotransmitter in the brain requires salt to move in and out of the cell [12]. Sodium is required to drive vitamin C into the brain and lower oxidative stress into the brain. People with mood issues have increased oxidative stress in the brain. Driving vitamin C into any organ is dependent on having enough sodium. Sodium is therefore vital for our neurotransmitters in the brain to work.

Salt plays a fundamental role in dozens of critical functions in our bodies.

Salt recommendations

Taste is a remarkable sense that can dictate our nutrient requirements. We have a stronger desire to eat salty foods when we have low sodium, and vice versa [13]. Salting to taste therefore is a great starting point for determining salt intake.

A 2011 study found that sodium intake of less than 3 grams of sodium per day or more than 6-7 grams of sodium per day both increased the risk of stroke and heart attack. However, sodium intake of between 4 and 6 grams of sodium each day was associated with the lowest risk of cardiovascular incidents [4].

When eating a healthy diet low in processed foods, it is important to make sure you are getting ENOUGH salt, since much of the salt intake in modern diets is found in processed foods. Exercise also increases one’s need for salt. Stress causes rapid wasting of sodium and so salt intake may need to be increased under times of stress.

Importantly, you should aim to have a potassium intake of over 3g per day. Potassium helps regulate sodium levels, and when we get too low potassium, we can start over-retaining salt. Potassium-rich foods include fruits, root vegetables, and leafy greens.

It is possible to take in too much salt if you are salt sensitive, which is typically driven by 3 primary factors: insulin resistance, low magnesium intake, and low potassium intake. The focus should be on addressing these factors instead of cutting out salt forever.

Does the type of salt matter? In general, it is much better to get any salt, even if it is regular table salt. However, there are benefits to unrefined salts. Sea salts and dessert salts contain minerals, such as magnesium, in trace amounts. There is a concern that consuming too much table salt can lead to mineral imbalances by delivering too much sodium and chloride to the cell and not enough of the other necessary minerals.

References

[1] L. K. Dahl, “Possible role of salt intake in the development of essential hypertension,” Int. J. Epidemiol., vol. 34, no. 5, 2005, doi: 10.1093/ije/dyh317.

[2] H. Bashyam, “Lewis Dahl and the genetics of salt-induced hypertension,” J. Exp. Med., vol. 204, no. 7, 2007, doi: 10.1084/jem.2047fta.

[3] P. Elliott et al., “The intersalt study: Main results, conclusions and some implications,” Clin. Exp. Hypertens., vol. A11, no. 5–6, 1989, doi: 10.3109/10641968909035389.

[4] M. J. O’Donnell et al., “Urinary sodium and potassium excretion and risk of cardiovascular events,” JAMA - J. Am. Med. Assoc., vol. 306, no. 20, 2011, doi: 10.1001/jama.2011.1729.

[5] K. Stolarz-Skrzypek et al., “Fatal and nonfatal outcomes, incidence of hypertension, and blood pressure changes in relation to urinary sodium excretion,” JAMA - J. Am. Med. Assoc., vol. 305, no. 17, 2011, doi: 10.1001/jama.2011.574.

[6] E. I. Ekinci et al., “Dietary salt intake and mortality in patients with type 2 diabetes,” Diabetes Care, vol. 34, no. 3, 2011, doi: 10.2337/dc10-1723.

[7] R. Garg, G. H. Williams, S. Hurwitz, N. J. Brown, P. N. Hopkins, and G. K. Adler, “Low-salt diet increases insulin resistance in healthy subjects,” Metabolism., vol. 60, no. 7, 2011, doi: 10.1016/j.metabol.2010.09.005.

[8] B. Renneboog, W. Musch, X. Vandemergel, M. U. Manto, and G. Decaux, “Mild chronic hyponatremia is associated with falls, unsteadiness, and attention deficits,” Am. J. Med., vol. 119, no. 1, 2006, doi: 10.1016/j.amjmed.2005.09.026.

[9] N. A. Graudal, A. M. Galløe, and P. Garred, “Effects of sodium restriction on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride: A meta-analysis,” Journal of the American Medical Association, vol. 279, no. 17. 1998, doi: 10.1001/jama.279.17.1383.

[10] R. HORTON and E. G. BIGLIERI, “Effect of aldosterone on the metabolism of magnesium.,” J. Clin. Endocrinol. Metab., vol. 22, 1962, doi: 10.1210/jcem-22-12-1187.

[11] F. Ahad and S. A. Ganie, “Iodine, Iodine metabolism and Iodine deficiency disorders revisited.,” Indian J. Endocrinol. Metab., vol. 14, no. 1, 2010.

[12] A. S. Pivovarov, F. Calahorro, and R. J. Walker, “Na+/K+-pump and neurotransmitter membrane receptors,” Invertebrate Neuroscience, vol. 19, no. 1. 2019, doi: 10.1007/s10158-018-0221-7.

[13] B. Lindemann, “Sodium taste,” Current Opinion in Nephrology and Hypertension, vol. 6, no. 5. 1997, doi: 10.1097/00041552-199709000-00003.